The present invention relates to a device for loading film on machines for wrapping products.
Current machines for wrapping groups of products (of the automatic or semi-automatic type) basically consist of a platform which supports the groups of products on a pallet (the platform may be rotary or fixed) and a structure which supports the film feed means. This structure may consist of a simple vertical column, on which a unit equipped with the above-mentioned film feed means (with rotary platform) slides in both directions, or may have horizontal arms or prongs which rotate about the group of products (usually with fixed platform).
The film feed means in turn consist of a film reel, rotatably mounted on a vertical shaft, which is attached to a plate which forms part of a feed means support carriage. In addition to the reel, there is a plurality of rollers, again with vertical axes attached to the plate, designed to allow the tensioned film to be guided and fed towards the group of products.
As well as these elements, in the current wrapping machines the use of motor-driven pre-stretching units for the wrapping film is increasingly common, especially when cold-stretch films are used. This pre-stretching procedure allows an increase in the film stabilising effect with a proportional reduction in the weight of the film on each group of products wrapped.
In order to obtain correct stretching of the film fed, that is to say, without the film sliding around the rollers and, above all, without a significant contraction or lateral reduction in the film web (which cancels out the reduction in film weight), the use of at least one pair of motor-driven rollers, independent of one another, is necessary in order to allow different peripheral speeds, with the two rollers positioned very close to one another and a large angle for film winding around the two rollers.
These operating conditions, together with the existing structure of the feed means, mean that the film feed unit has a large number of rollers which are very close to one another on the drive carriage. This architecture, therefore, makes it difficult for the operator to load or insert the film (when the reel ends or if the film breaks), since the spaces between rollers are very limited and there is also sometimes a danger that the operator""s fingers may be crushed when manually inserting the end of the film.
In an attempt to overcome these disadvantages, the manufacturers of these machines designed a first solution consisting of a carriage which supports the reel and the guide and pre-stretching rollers in a cantilever configuration, that is to say using only a support rod. This architecture partly solves the problem of loading the film in the rollers (one end of the rollers is free), but requires precision sizing of the single support part and extremely stiff rollers (since there is only one resting point) which considerably raises the cost of the machine, as well as complicating assembly. In addition, the transmission and roller speed adjustment parts (variable speed motors and pulley/gear units) are concentrated at one end of the rollers, making the longitudinal dimension of the roller carriage very large and the configuration of the mechanisms which transmit motion to the rollers complex.
In a second solution, the support carriage was split into a fixed part and a mobile part, that is to say, a part which turns about a horizontal or vertical pivot axis. This solution allows the operator to load the film, after turning the mobile part, by threading the end of the film into the free area of the fixed part.
However, the second solution also has disadvantages, due to the increased size and weight of the carriage, necessary in order to split it, with the consequent use of lifting parts suitable for this purpose, thus raising the cost of unit production. In this solution, the pre-stretching rollers must also be moved away from one another, and it is possible to reduce the winding angles, with the consequent risks that the quality of the pre-stretching operation may be lowered.
The aim of the present invention is, therefore, to overcome the above-mentioned disadvantages by providing a device for loading film which has an extremely compact structure, but which can be used at high speed and allows the operator to rapidly insert the end of the film between the pre-stretching rollers, whilst maintaining production levels similar to that of conventional machines.